1. Field of the Invention
The present invention is directed to a method for controlling the column-by-column printing of a franking image or impression in a postage meter machine, whereby the image data are kept ready in encoded form and are converted into binary signals for driving printer elements before a printing event.
2. Description of the Prior Art
In this known method of the type described above, a franking image in the form of coded image data is stored in a memory for every possible postage value. When printing the franking image on an envelope, the envelope is passed under a printer head whose printer elements are arranged in a column transversely relative to the conveying direction. A franking image having a suitable postage value is selected and printed dependent on the weight of the letter or on the size of the envelope. Before or during the column-by-column printing, the coded image data are decoded, converted into binary data and binary signals for driving the printer elements are produced therefrom. When many different postage values occur or when the franking image is to contain other variable image parts such as, for example, a date, then a memory having a large storage capacity, or a large number of electronic memory modules must be provided for storing the coded image data. This requires space to be reserved for the memory or modules in a postage meter machine, and thus increases the technical outlay and costs.
Another disadvantage is that the conversion of the coded image information for an entire franking image is relatively time-consuming. The time required for coding lengthens the time between two impressions in a postage meter machine, so that the throughput of letters per time unit is limited.
U.S. Pat. No. 4,580,144 discloses a method wherein the franking image is composed of two sub-images. A constant image part (one sub-image) is printed on an envelope by a first printing station. The postage value (the other sub-image), that can vary dependent on the letter, is printed by a second printing station. The image data for the variable image part are in encoded form and are converted into binary signals at the printing event for driving printer elements of a thermo-transfer printing head. The printing speed for the overall impression can be increased by the division of the franking image to be printed into two partial images. Since two printer heads are utilized in this known solution, however, the technological outlay is high.
German OS 40 34 292 discloses a printing method wherein a permanently prescribed part of the franking image is stored in the memory in the postage meter machine, whereas another part is kept ready in a data processing system arranged at a remote from the postage meter machine. Data of the permanently prescribed part are transmitted from the data processing system to the postage meter machine and are combined at the postage meter machine before the printing. The data of the permanently prescribed part of the franking image are stored in a non-volatile memory.
Further, German OS 37 12 100 discloses a postage meter machine message printing system wherein the postage meter machine has a memory for advertising messages. These advertising messages can be modified, for which purpose printing data are transmitted to the memory from a remote station.
Further, European Application 0 352 498 discloses a postage meter machine having a first memory that stores fixed data of a print format that is repeated at every franking. Variable data are stored in a second memory. The data of the two memories are superimposed on one another for printing.